It is well known that well streams containing a mixture of fluids such as crude oil, condensate, formation water and gas during transportation may react and form solid hydrates resulting in i.e. blocked pipelines. To avoid and or limit the formation of hydrates compounds known as hydrate inhibitors are added to the well stream prior to transportation. One example of an often applied hydrate inhibitor is mono-ethylene glycol (MEG), other applicable hydrate inhibitors include glycol compounds with other substituents, as well as kinetic hydrate inhibitors or combinations thereof. The term kinetic refers to the effect of the inhibitor lowering the reaction rate of the hydrate forming reactions.
Hydrate inhibitors such as MEG are valuable chemicals and the recycling thereof provides reduced costs. However equally important are the environmental consequences, as waste streams containing not inconsiderable amounts of MEG or similar inhibitors can not be released to the environment.
A number of different steps and methods for separating MEG for reuse are known in the art.
After a first separation of hydrocarbons the process fluid normally comprises a hydrocarbon rest, water, corrosion products, MEG and dissolved mineral salts. Normally the amount of mineral salts is considerable and the salts may precipitate during the MEG extraction process which again leads to increased viscosity, sludge formation or plugging. Depending on the formation the composition of the mineral salts will vary. It is well known to remove salts from solutions by precipitation of solids by increasing the activity or concentration; however the combination of alkali and earth alkali ions, and halogen, carbonate and bicarbonate ions results in the precipitation of relatively small salt particles that are not easily separated from the solution. A further obstacle for the regeneration process is degradation of the inhibitor at high temperatures which limits the heating possibility to obtain separation.